Method and apparatus for transmitting downlink signal in a MIMO wireless communication system

ABSTRACT

A method and apparatus for transmitting a downlink signal in a multiple input multiple output (MIMO) wireless communication system is disclosed. A method for receiving a downlink signal from a base station to a user equipment in a multiple input multiple output (MIMO) system, which supports dual layer transmission based on first and second antenna ports, comprises receiving downlink control information (DCI) through a downlink control channel; and receiving downlink data through a downlink data channel, the downlink data including one or more of a first transport block and a second transport block, wherein the downlink control information includes a new data indicator (NDI) for each of the first and second transport blocks, and if the first transport block is disabled and the second transport block is enabled, the new data indicator for the first transport block indicates an antenna port through which the second transport block is received.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. §119, this application claims the benefit ofearlier filing date and right of priority to Korean Patent ApplicationNo. 10-2010-0027988, filed on Mar. 29, 2010, and also claims the benefitof U.S. Provisional Application Nos. 61/241,969, filed on Sep. 14, 2009,61/242,286, filed on Sep. 14, 2009, 61/250,854, filed on Oct. 12, 2009,and 61/297,430, filed on Jan. 22, 2010, the contents of which are allincorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for transmitting a downlinksignal in a multiple input multiple output (MIMO) wireless communicationsystem.

2. Discussion of the Related Art

In a mobile communication system, a user equipment can receiveinformation from a base station through a downlink. Also, the userequipment can transmit information to the base station through anuplink. Examples of the information transmitted from and received in theuser equipment include data and various kinds of control information.Various physical channels exist depending on types and usage of theinformation transmitted from and received in the user equipment.

A multiple input multiple output (MIMO) scheme means that a base stationand a user equipment simultaneously transmit several data streamsspatially by using two or more transmitting/receiving antennas so as toincrease system capacity. The MIMO schemes can implement transmitdiversity, spatial multiplexing or beamforming by using severaltransmitting antennas.

The transmit diversity scheme is advantageous in that same datainformation is transmitted through several transmitting antennas toimplement data transmission of high reliability without channel feedbackfrom a receiver. The beamforming scheme is used to increase a receivedsignal to interference plus noise ratio (SINR) of a receiver bymultiplying several transmitting antennas by proper weight values.Generally, since uplink/downlink channels are independent in a frequencydivision duplexing (FDD) system, channel information of high reliabilityis required to obtain proper beamforming gain. In this case, the channelinformation is separately fed back from a receiver.

Meanwhile, the spatial multiplexing scheme can be divided into a singleuser spatial multiplexing scheme and a multi-user spatial multiplexingscheme. The single user spatial multiplexing scheme is referred to as aspatial multiplexing (SM) or single user MIMO (SU-MIMO). In the singleuser spatial multiplexing scheme, a plurality of antenna resources of abase station are allocated to a single user (user equipment), andcapacity of a MIMO channel increases in proportion to the number ofantennas. Meanwhile, the multi-user spatial multiplexing scheme isreferred to as spatial divisional multiple access (SDMA) or multi-userMIMO (MU-MIMO). In the multi-user spatial multiplexing scheme, aplurality of antenna resources of a base station or radio spatialresources are distributed to a plurality of users (user equipments).

Examples of the MIMO scheme include a Single CodeWord (SCW) scheme and aMultiple CodeWord (MCW) scheme, wherein the SCW scheme is intended totransmit N number of data streams at the same time by using singlechannel encoding block, and the MCW scheme is intended to transmit Nnumber of data streams by using M (M is always smaller than or equal toN) number of channel encoding blocks. In this case, each channelencoding block generates independent codewords, each of which isdesigned to enable independent error detection.

Meanwhile, a downlink control channel can include a control signal thatdefines resource allocation and transport format in respect of a signaltransmitted through a downlink data channel. In the 3GPP LTE (long termevolution) standard, the downlink control channel and the downlink datachannel are referred to as a physical downlink control channel (PDCCH)and a physical downlink shared channel (PDSCH), respectively, andcontrol information transmitted through the PDCCH is referred to asdownlink control information (DCI).

The base station determines a PDCCH format in accordance with DCIintended to be transmitted to a user equipment, and adds cyclicredundancy check (CRC) to control information. The CRC is masked with aunique identifier (referred to as radio network temporary identifier(RNTI) in accordance with an owner or usage of the PDCCH. If the PDCCHis for a specific user equipment, the CRC is masked with a uniqueidentifier of the user equipment, for example, C-RNTI (Cell-RNTI). IfC-RNTI is used, the PDCCH carries control information for thecorresponding specific user equipment. If another RNTI is used, thePDCCH carries common control information received by all user equipmentsor a plurality of user equipments within the cell.

After CRC is added to the DCI, channel coding, rate matching andmodulation are performed, and the modulated symbols are mapped withphysical resource elements and then transmitted to the user equipment.The user equipment monitors a plurality of PDCCHs per subframe. In thiscase, monitoring means that the user equipment tries to decode each ofthe PDCCHs in accordance with a DCI format which is monitored. In acontrol region allocated within a subframe, the base station does notprovide the user equipment with information as to where thecorresponding PDCCH is. The user equipment discovers its PDCCH bymonitoring a collection of PDCCH candidates within the subframe. Thiswill be referred to as blind decoding. For example, if the userequipment performs de-masking for its C-RNTI in the corresponding PDCCHand does not detect any CRC error, it detects a PDCCH having its DCI.The user equipment can be set semi-statically through upper layersignaling to receive PDSCH data signaled through the PDCCH subject tovarious transmission modes.

In order to receive a downlink signal, the user equipment receives adownlink resource on the PDCCH. If the user equipment successfullydetects the PDCCH, it reads DCI on the PDCCH. The user equipment canreceive downlink data on the PDSCH by using downlink resource allocationwithin the DCI.

In downlink signal transmission according to the aforementioned MIMOscheme, the base station can transmit control information as DCI throughthe PDCCH, wherein the control information is intended to allow the userequipment to normally receive a downlink signal. In case of downlinksignal transmission that uses a new MIMO scheme different from theexisting MIMO scheme, a problem may occur in that the user equipmentfails to normally receive a downlink signal through control informationsubject to a DCI format defined previously. Accordingly, in a newdownlink MIMO transmission scheme, it is required that controlinformation required to normally receive a downlink signal should beprovided to the user equipment.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method and apparatusfor transmitting a downlink signal in a multiple input multiple output(MIMO) wireless communication system, which substantially obviates oneor more problems due to limitations and disadvantages of the relatedart.

An object of the present invention is to provide a method and apparatusfor transmitting a downlink signal in a multiple input multiple output(MIMO) wireless communication system.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, inone aspect of the present invention, a method for receiving a downlinksignal from a base station to a user equipment in a multiple inputmultiple output (MIMO) system, which supports dual layer transmissionbased on first and second antenna ports, comprises receiving downlinkcontrol information (DCI) through a downlink control channel; andreceiving downlink data through a downlink data channel, the downlinkdata including one or more of a first transport block and a secondtransport block, wherein the downlink control information includes a newdata indicator (NDI) for each of the first and second transport blocks,and if the first transport block is disabled and the second transportblock is enabled, the new data indicator for the first transport blockindicates an antenna port through which the second transport block isreceived.

Also, the new data indicator is given by 1 bit, if the new dataindicator for the first data block is a first value, it indicates thefirst antenna port, and if the new data indicator for the first datablock is a second value, it indicates the second antenna port.

Also, the second transport block is mapped with one of first and secondcodewords, one codeword mapped with the second transport block is mappedwith one of first and second layers, and one layer mapped with onecodeword, which is mapped with the second transport block, correspondsto one of the first and second antenna ports.

Also, the downlink control information further includes modulation andcoding scheme (MCS) and redundancy version (RV) for each of the firstand second transport blocks, and one or more of the modulation andcoding scheme (MCS) and the redundancy version (RV) indicate whether acorresponding transport block is disabled.

Also, the method further comprises receiving a UE-specific referencesignal for demodulating the downlink data for one or more of the firstand second antenna ports.

Also, the downlink data channel is a physical downlink common channel(PDSCH), and the downlink control channel is a physical downlink controlchannel (PDSCH).

In another aspect of the present invention, a method for transmitting adownlink signal from a base station to a user equipment in a multipleinput multiple output (MIMO) system, which supports dual layertransmission based on first and second antenna ports, comprisestransmitting downlink control information (DCI) through a downlinkcontrol channel; and transmitting downlink data through a downlink datachannel, the downlink data including one or more of a first transportblock and a second transport block, wherein the downlink controlinformation includes a new data indicator (NDI) for each of the firstand second transport blocks, and if the first transport block isdisabled and the second transport block is enabled, the new dataindicator for the first transport block indicates an antenna portthrough which the second transport block is transmitted.

Also, the new data indicator is given by 1 bit, if the new dataindicator for the first data block is a first value, it indicates thefirst antenna port, and if the new data indicator for the first datablock is a second value, it indicates the second antenna port.

Also, the second transport block is mapped with one of first and secondcodewords, one codeword mapped with the second transport block is mappedwith one of first and second layers, and one layer mapped with onecodeword, which is mapped with the second transport block, correspondsto one of the first and second antenna ports.

Also, the downlink control information further includes modulation andcoding scheme (MCS) and redundancy version (RV) for each of the firstand second transport blocks, and one or more of the modulation andcoding scheme (MCS) and the redundancy version (RV) indicate whether acorresponding transport block is disabled.

Also, the method further comprises transmitting a UE-specific referencesignal for demodulating the downlink data for one or more of the firstand second antenna ports.

Also, the downlink data channel is a physical downlink common channel(PDSCH), and the downlink control channel is a physical downlink controlchannel (PDSCH).

In still another aspect of the present invention, a user equipment forreceiving a downlink signal from a base station in a multiple inputmultiple output (MIMO) system, which supports dual layer transmissionbased on first and second antenna ports, comprises a receiving modulereceiving control information and data from the base station; atransmitting module transmitting control information and data to thebase station; and a processor connected with the receiving module andthe transmitting module, controlling the user equipment, which includesthe receiving module and the transmitting module, wherein the processorperforms a control operation so that the receiving module receivesdownlink control information (DCI) through a downlink control channel,and receives downlink data through a downlink data channel, the downlinkdata including one or more of first and second transport blocks, thedownlink control information includes a new data indicator (NDI) foreach of the first and second transport blocks, and if the firsttransport block is disabled and the second transport block is enabled,the new data indicator for the first transport block indicates anantenna port through which the second transport block is received.

In further still another aspect of the present invention, a base stationfor transmitting a downlink signal to a user equipment in a multipleinput multiple output (MIMO) system, which supports dual layertransmission based on first and second antenna ports, comprises areceiving module receiving control information and data from the userequipment; a transmitting module transmitting control information anddata to the user equipment; and a processor connected with the receivingmodule and the transmitting module, controlling the base station, whichincludes the receiving module and the transmitting module, wherein theprocessor performs a control operation so that the transmitting moduletransmits downlink control information (DCI) through a downlink controlchannel, and transmits downlink data through a downlink data channel,the downlink data including one or more of first and second transportblocks, the downlink control information includes a new data indicator(NDI) for each of the first and second transport blocks, and if thefirst transport block is disabled and the second transport block isenabled, the new data indicator for the first transport block indicatesan antenna port through which the second transport block is transmitted.

A method for efficiently configuring downlink control informationrequired for downlink MIMO transmission is provided.

It is to be understood that the advantages that can be obtained by thepresent invention are not limited to the aforementioned advantages andother advantages which are not mentioned will be apparent from thefollowing description to the person with an ordinary skill in the art towhich the present invention pertains.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a block diagram illustrating a structure of a downlink MIMOsystem according to the related art;

FIG. 2 is a diagram illustrating a mapping relation between a layer anda physical antenna in a downlink MIMO structure;

FIG. 3 is a diagram illustrating a downlink control information (DCI)format 2A used in the present invention;

FIG. 4 is a diagram illustrating a DCI format 1A used in the presentinvention;

FIG. 5 is a diagram illustrating a DCI format 1D used in the presentinvention;

FIG. 6 is a diagram illustrating a new DCI format according to oneembodiment of the present invention;

FIG. 7 is a diagram illustrating a new DCI format according to anotherembodiment of the present invention;

FIG. 8 is a diagram illustrating a new DCI format according to otherembodiment of the present invention;

FIG. 9 is a diagram illustrating a configuration of a preferredembodiment of a user equipment according to the present invention; and

FIG. 10 is a diagram illustrating a configuration of a preferredembodiment of a base station according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

The following embodiments are achieved by combination of structuralelements and features of the present invention in a predetermined type.Each of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. Also, some structural elements and/orfeatures may be combined with one another to constitute the embodimentsof the present invention.

The embodiments of the present invention have been described based onthe data transmission and reception between a base station and a userequipment. In this case, the base station means a terminal node of anetwork that performs direct communication with the user equipment. Aspecific operation which has been described as being performed by thebase station may be performed by an upper node of the base station asthe case may be.

In other words, it will be apparent that various operations performedfor communication with the user equipment in the network which includesa plurality of network nodes along with the base station can beperformed by the base station or network nodes other than the basestation. The base station may be replaced with terms such as a fixedstation, Node B, eNode B (eNB), and access point (AP). Also, a relaydevice may be replaced with terms such as a relay node (RN) and a relaystation (RS). Also, a terminal may be replaced with terms such as userequipment (UE), a mobile station (MS), a mobile subscriber station(MSS), and a subscriber station (SS).

Specific terminologies hereinafter described are provided to assistunderstanding of the present invention, and various modifications can bemade in the specific terminologies within the range that they do notdepart from technical spirits of the present invention.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

The embodiments of the present invention can be supported by standarddocuments disclosed in at least one of wireless access systems, i.e.,IEEE 802 system, 3GPP system, 3GPP LTE system, and 3GPP2 system. Namely,among the embodiments of the present invention, steps or parts which arenot described to clarify technical spirits of the present invention canbe supported by the above standard documents. Also, all terminologiesdisclosed herein can be described by the above standard documents.

The following technology can be used for various wireless access systemssuch as CDMA (code division multiple access), FDMA (frequency divisionmultiple access), TDMA (time division multiple access), OFDMA(orthogonal frequency division multiple access), and SC-FDMA (singlecarrier frequency division multiple access). The CDMA can be implementedby radio technology such as universal terrestrial radio access (UTRA) orCDMA2000. The TDMA can be implemented by radio technology such as globalsystem for mobile communications (GSM)/general packet radio service(GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMA can beimplemented by radio technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16(WiMAX), IEEE 802.20, and evolved UTRA (E-UTRA). The UTRA is a part of auniversal mobile telecommunications system (UMTS). A 3^(rd) generationpartnership project long term evolution (3GPP LTE) communication systemis a part of an evolved UMTS (E-UMTS) that uses E-UTRA, and uses OFDMAin a downlink while uses SC-FDMA in an uplink. LTE-advanced (LTE-A) isan evolved version of the 3GPP LTE. WiMAX can be described by the IEEE802.16e standard (WirelessMAN-OFDMA Reference System) and the advancedIEEE 802.16m standard (WirelessMAN-OFDMA Advanced system).

Although the following description will be based on the 3GPP LTEstandard to clarify description, it is to be understood that technicalspirits of the present invention are not limited to the 3GPP LTEstandard.

MIMO (multiple input multiple output) technology can improvetransmission and reception efficiency of data by using multipletransmitting antennas and multiple receiving antennas. The MIMOtechnology includes a spatial multiplexing, transmit diversity, andbeamforming. A MIMO channel matrix subject to the number of receivingantennas and the number of transmitting antennas can be divided into aplurality of independent channels. Each independent channel will bereferred to as a layer or stream. The number of layers or streams or aspatial multiplexing rate will be referred to as a rank.

The existing MIMO system is designed based on a Multiple CodeWord (MCW)scheme. The MCW scheme allows that two codewords are transmitted at thesame time. For such MIMO transmission, modulation and coding scheme(MCS) information used by a transmitter, a new data indicator indicatingwhether transmitted data are new data or retransmission data, andredundancy version (RV) information as to what sub-packet isretransmitted in case of retransmission will be required.

FIG. 1 is a block diagram illustrating a structure of a downlink MIMOsystem according to the related art. In the system that supports a MIMOscheme, a base station can transmit one or more codewords to a downlink.The codewords are mapped with a transport block from an upper layer andwill be described later. FIG. 1 exemplarily illustrates a system thatsupports maximum two codewords. One or more codewords can be processedas complex symbols through a scrambling module and a mapper. Then, thecomplex symbols are mapped with a plurality of layers by a layer mapper,wherein each layer is multiplied by a predetermined precoding matrixselected by a precoding module depending on a channel status and thencan be allocated to each transmitting antenna. The transmission signalprocessed above for each antenna is mapped with a time-frequencyresource element to be used for transmission by a resource elementmapper, and then transmitted through an OFDM signal generator and eachantenna in due order.

A transport block to codeword mapping rule will be described. In FIG. 1,two transport blocks (TBs) are mapped with two codewords by thetransport block to codeword mapping rule. This mapping rule can beconfigured as illustrated in Table 1 and Table 2 below in accordancewith a TB to CW swap flag.

TABLE 1 TB to CW swap flag value CW 0 (enabled) CW 1 (enabled) 0 TB 1 TB2 1 TB 2 TB 1

TABLE 2 TB 1 TB 2 CW 0 (enabled) CW 1 (disabled) enabled disabled TB 1 —disabled enabled TB 2 —

Table 1 illustrates that two transport blocks are enabled, and Table 2illustrates an example of a transport block to codeword mapping rulewhen any one of two transport blocks is enabled and the other one isdisabled.

In Table 2, in the case that the transport block is disabled, the sizeof the transport block is 0. If the size of the transport block is 0,the corresponding transport block is not mapped with a codeword.

If signal transmission is performed using a single antenna, one codewordis mapped with one layer and then transmitted. However, if signaltransmission is performed using multiple antennas, a codeword-to-layermapping rule can be configured as illustrated in Table 3 and Table 4below in accordance with a transmission mode.

TABLE 3 Number of code Codeword-to-layer mapping Number of layers wordsi = 0, 1, . . . , M_(symb) ^(layer) − 1 1 1 x⁽⁰⁾(i) = d⁽⁰⁾(i) M_(symb)^(layer) = M_(symb) ⁽⁰⁾ 2 2 x⁽⁰⁾(i) = d⁽⁰⁾(i) M_(symb) ^(layer) =M_(symb) ⁽⁰⁾ = M_(symb) ⁽¹⁾ x⁽¹⁾(i) = d⁽¹⁾(i) 2 1 x⁽⁰⁾(i) = d⁽⁰⁾(2i)M_(symb) ^(layer) = M_(symb) ⁽⁰⁾/2 x⁽¹⁾(i) = d⁽⁰⁾(2i + 1) 3 2 x⁽⁰⁾(i) =d⁽⁰⁾(i) M_(symb) ^(layer) = M_(symb) ⁽⁰⁾ = M_(symb) ⁽¹⁾/2 x⁽¹⁾(i) =d⁽¹⁾(2i) x⁽²⁾(i) = d⁽¹⁾(2i + 1) 4 2 x⁽⁰⁾(i) = d⁽⁰⁾(2i) M_(symb) ^(layer)= M_(symb) ⁽⁰⁾/2 = M_(symb) ⁽¹⁾/2 x⁽¹⁾(i) = d⁽⁰⁾(2i + 1) x⁽²⁾(i) =d⁽¹⁾(2i) x⁽³⁾(i) = d⁽¹⁾(2i + 1)

TABLE 4 Number Number of of code Codeword-to-layer mapping layers wordsi = 0, 1, . . . , M_(symb) ^(layer) − 1 2 1 x⁽⁰⁾ (i) = d⁽⁰⁾ (2i) x⁽¹⁾(i) = d⁽⁰⁾ (2i + 1) M_(symb) ^(layer) = M_(symb) ⁽⁰⁾/2 4 1 x⁽⁰⁾ (i) =d⁽⁰⁾ (4i) x⁽¹⁾ (i) = d⁽⁰⁾ (4i + 1) x⁽²⁾ (i) = d⁽⁰⁾ (4i + 2) x⁽³⁾ (i) =d⁽⁰⁾ (4i + 3) $M_{symb}^{layer} = \left\{ {{\begin{matrix}{M_{symb}^{(0)}/4} & {{{if}\mspace{14mu} M_{symb}^{(0)}\mspace{11mu}{mod}{\;\;}4} = 0} \\{\left( {M_{symb}^{(0)} + 2} \right)/4} & {{{if}\mspace{14mu} M_{symb}^{(0)}\mspace{11mu}{mod}{\;\;}4} \neq 0}\end{matrix}{If}\mspace{14mu} M_{symb}^{(0)}\mspace{11mu}{mod}\mspace{11mu} 4} \neq {0\mspace{14mu}{two}\mspace{14mu}{null}\mspace{14mu}{symbols}\mspace{14mu}{shall}\mspace{14mu}{be}{appended}\mspace{14mu}{to}\mspace{14mu}{d^{(0)}\left( {M_{symb}^{(0)} - 1} \right)}}} \right.$

Table 3 illustrates an example of signal transmission according to aspatial multiplexing scheme, and Table 4 illustrates an example ofsignal transmission according to a transmit diversity scheme. Also, inTable 3 and Table 4, x^((a))(i) represents the ith symbol of a layerhaving index a, and d^((a))(i) represents the ith symbol of a codewordhaving index a. A mapping rule between the number of codewords and thenumber of layers can be identified through ‘Number of layers’ and‘Number of codewords’ in Table 3 and Table 4. Also, ‘codeword-to-Layermapping’ represents how symbols of each codeword are mapped with alayer.

As noted in Table 3 and Table 4, although one codeword is mapped withone layer in a symbol unit and then transmitted, one codeword may bedistributively mapped with maximum four layers as illustrated in thesecond example of Table 4.

A layer to physical antenna mapping rule will be described withreference to FIG. 2. The following description is only exemplary, andthe layer to physical antenna mapping rule can have a random type. Inthe following description, it is assumed that a system that supports aMIMO transmission scheme has four physical transmitting antennas, forexample. If rank is 1, one codeword CW1 is mapped with one layer, anddata generated by one layer in accordance with a precoding scheme can beencoded to be transmitted through four transmitting antennas. If rank is2, two codewords CW1 and CW2 are mapped with two layers and mapped withfour transmitting antennas by a precoder. Also, if rank is 3, onecodeword CW1 of two codewords is mapped with one layer, and the otherone CW2 is mapped with two layers by a serial-to-parallel converter (S/Pconverter), whereby a total of two codewords are mapped with threelayers and then mapped with four transmitting antennas by a precoder.Moreover, if rank is 4, two codewords CW1 and CW2 are respectivelymapped with two layers by the serial-to-parallel converter, whereby atotal of four layers are mapped with four transmitting antennas by theprecoder.

Although a base station having four transmitting antennas can havemaximum four layers and four independent codewords, FIG. 2 illustratesan example of a system having maximum two codewords. Also, location ofinformation transmitted through the codeword CW1 and location ofinformation transmitted through the codeword CW2 may be changed to eachother.

Meanwhile, the precoder is represented by Mt (the number of transmittingantennas)*v (spatial multiplexing rate) matrix, and adaptively uses aprecoding matrix by using a collection of matrixes defined previously bya transmitter/receiver. A collection of these precoding matrixes will bereferred to as a codebook.

In the existing 3GPP LTE system, four or more physical antenna ports(for example, antenna ports 0 to 5) can be used. In this case,identification of antenna ports is not physical identification.Accordingly, logical antenna index to physical antenna index mapping isvaried depending on options of each manufacturer. It is not necessarilyrequired that an antenna port should correspond to a physical antennaone to one. One antenna port may correspond to one physical antenna oran antenna array which is combination of a plurality of physicalantennas.

In the 3GPP LTE system, three types of downlink reference signals areused. Namely, examples of the downlink reference signal include acell-specific reference signal (having no relation with MBSFNtransmission), an MBSFN reference signal related to MBSFN transmission,and a UE-specific reference signal.

The cell-specific reference signal is a reference signal based on asequence generated using each cell ID as an initial value. Forcell-specific reference signal transmission, antenna ports 0 to 3 can beused. Also, the MBSFN reference signal is used to acquire downlinkchannel information for MBSFN transmission, and is a reference signaltransmitted through antenna port 4.

The UE-specific reference signal is supported for single antenna porttransmission of a PDSCH, and can be transmitted through antenna port 5.The user equipment (UE) can be transferred from an upper layer (aboveMAC layer) whether the UE-specific reference signal can be used forPDSCH demodulation. The UE-specific reference signal enables beamformingof data transmission for a specific user equipment. For example, thebase station can generate directivity transmission for a specific userequipment by using an array (one antenna port) of physical antennas,which are located near the base station. Signals from different physicalantennas have phases appropriately set and can be joined together at thelocation of the user equipment. This directivity transmission isrecognized by the user equipment as one antenna. Since a beam formed bybeamforming suffers different channel responses between the base stationand the user equipment, the UE-specific reference signal is requiredsuch that the user equipment normally demodulates beamformed data.

The aforementioned UE-specific reference signal corresponds to adedicated reference signal (DRS) or a precoded demodulation referencesignal (DMRS). If the precoded DMRS is used, the reference signalsequivalent to a spatial multiplexing rate are transmitted.

The UE-specific reference signal may be used as single layer beamforming(beamforming of rank 1 transmission). As described above, since theUE-specific reference signal is precoded by the same precoder as thatapplied to data on the PDSCH, a precoding matrix is transparent to theuser equipment. In other words, in case of transmission based on theUE-specific reference signal, since an estimated channel includes aprecoding weight value, single layer beamforming can be implementedwithout precoding information. DCI format 1 or DCI format 1A of theaforementioned DCI format, which is defined for single antenna porttransmission and transmit diversity, can be used for the single layerbeamforming.

Meanwhile, in the existing 3GPP LTE (Release 8) system, since onlyantenna port 5 is defined as an antenna port to which the UE-specificreference signal is transmitted, data transmission using cell-specificreference signals (antenna ports 0 to 3) is required if rank is morethan 2. In other words, each user equipment can perform datademodulation by using channel information acquired through thecell-specific reference signal and precoding weight information acquiredthrough a control channel.

Recently, in the 3GPP LTE Release 9, dual layer beamforming (or dualstream beamforming) has been discussed. Dual layer beamforming means aMIMO transmission scheme that supports transmission of maximum rank 2based on the UE-specific reference signal, and corresponding extensionof the aforementioned single layer beamforming. According to the duallayer beamforming, maximum two enabled transport blocks are respectivelywith two codewords and then transmitted through two layers, and adedicated reference signal for each layer is transmitted. According tothe dual layer beamforming, even though the base station does not notifyeach user equipment of precoding information, the user equipment canreceive MIMO transmission from the base station without multi-userinterference by using channel information acquired through theUE-specific reference signal transmitted to each layer.

The dedicated reference signal for dual layer beamforming can bedesigned such that respective layers are orthogonal to each other,through a scheme such as time division multiplexing (TDM)/frequencydivision multiplexing (FDM)/code division multiplexing (CDM). Iftransmission is performed using a single layer only, one of dedicatedreference signals that support two layers, which corresponds to singlelayer transmission, is notified, whereby throughput for datademodulation can be improved. Accordingly, a bit field indicating areference signal used for single layer beamforming in downlink controlinformation is required.

Also, according to the dual layer beamforming, data can be transmittedand received through two layers or a single layer. If differentcodewords are transmitted through two layers, it corresponds to multiplecodeword single user-multiple input multiple output (MCW SU-MIMO). Incase of single layer transmission, the user equipment can be operated inaccordance with SU-MIMO or MU-MIMO. If data are transmitted to a singleuser by using a single layer, it corresponds to SU-MIMO. If two layersare respectively allocated to different users, it corresponds toMU-MIMO. In case of MU-MIMO, since each user equipment should divide therespective layers by using channel information acquired through theUE-specific reference signal, the base station can provide each userequipment with information indicating a layer corresponding to each userequipment, whereby the user equipment can acquire a channel. Asdescribed above, in the dual layer beamforming scheme, since maximum twolayers are used, it is noted that 1-bit information is required toindicate one of two layers through the base station.

Hereinafter, new definition of a field, which is defined in the existingDCI format, to support dual layer beamforming in accordance with theembodiment of the present invention will be described. In the existing3GPP LTE standard (for example, 3GPP LTE Release 8), DCI formats 0, 1,1A, 1B, 1C, 1D, 2, 2A, 3 and 3A are defined. In brief, DCI format 0represents uplink resource allocation information, DCI formats 1˜2represent downlink resource allocation information, DCI formats 3 and 3Arepresent uplink TPC(transmit power control) command for random UEgroups.

FIG. 3 is a diagram illustrating a downlink control information (DCI)format 2A used in the present invention. The DCI format 2A correspondsto a control information format for opened-loop spatial multiplexingtransmission. Opened-loop spatial multiplexing transmission means thatspatial multiplexing transmission is performed without feedback from theuser equipment.

The DCI format 2A supports maximum two codewords (transport blocks), anddefines MCS, NDI, and RV for each transport block. As described above,the MCS is information of a modulation and coding scheme used by atransmitter, the NDI is a new data indicator indicating whethertransmitted data are new data or retransmitted data, and RV meansredundancy version information as to what sub-packet is retransmitted incase of retransmission. Meanwhile, a transport block to codeword swapflag, as illustrated in Table 1, represents swap as to mapping of twotransport blocks to two codewords.

Precoding information defined in the DCI format 2A provides informationof transmission rank. The precoding information is set to 0 bit (i.e.,no precoding information exists) in case of transmission using twoantenna ports, and is set to 2 bits in case of transmission using fourantenna ports. A precoding information field for four antenna ports canbe defined as illustrated in Table 5 below.

TABLE 5 One codeword: Two codewords: Codeword 0 enabled, Codeword 0enabled, Codeword 1 disabled Codeword 1 enabled Bit Bit field fieldmapped mapped to to index Message index Message 0 4 layers: Transmit 0 2layers: precoder diversity cycling with large delay CDD 1 2 layers:precoder 1 3 layers: precoder cycling with large cycling with largedelay CDD delay CDD 2 reserved 2 4 layers: precoder cycling with largedelay CDD 3 reserved 3 reserved

According to the DCI format 2A, transmit diversity transmission isperformed in case of rank 1 (one codeword is enabled), and spatialmultiplexing transmission having two codewords is performed in case ofrank 2. Rank indication may be performed explicitly or implicitly.Explicit rank indication can be performed by a method for defining aseparate rank indicator.

Meanwhile, the user equipment may acquire rank information implicitlywithout defining a rank indicator. In this case, whether the transportblock is enabled or disabled can be indicated by MCS information and RVof the transport block. In the DCI format 2A, if MCS index value of thetransport block is set to 0, for example, to represent the size of thetransport block is 0, it means that transmission is not performed.Accordingly, the MCS information of the transport block indicates thatthe transport block is disabled. If the size of the transport block isnot 0, it indicates that the transport block is enabled. Also, if theMCS index value is se to 0 and RV is set to 1, it indicates that thetransport block is disabled. In other cases, it indicates that thetransport block is enabled. Accordingly, the user equipment canimplicitly identify that rank 2 transmission is performed if twotransport blocks are enabled while rank 1 transmission is performed ifone of two transport blocks is enabled and the other one is disabled.

New definition of a part of a bit field of the aforementioned DCI format2A in accordance with one embodiment of the present invention will bedescribed.

In the first embodiment, the transport block to codeword swap flag isused as a codeword indicator.

According to definition of the existing DCI 2A format, if one of twotransport blocks is enabled, the transport block to codeword swap flagis reserved and the transport blocks 1 and 2 are mapped with codeword 0(see Table 2). This embodiment suggests a method for using a transportblock to codeword swap flag as an indicator of codeword mapped with onetransport block if one of two transport blocks is enabled. In otherwords, the transport block to codeword swap flag can be reused asinformation indicating index of codeword used for single layerbeamforming.

According to this embodiment, in a state that only one of two transportblocks is enabled, the transport block to codeword swap flag is notreserved and 1 bit value is given. In a state that only one of twotransport blocks is enabled and the logic value of the swap flag is afirst value, if the enabled transport block is transport block 1, thetransport block 1 is mapped with codeword 0. If the enabled transportblock is transport block 2, the transport block 2 is mapped withcodeword 1. Meanwhile, in a state that only one of two transport blocksis enabled and a logic value of the swap flag is a second value, if theenabled transport block is transport block 1, the transport block 1 ismapped with codeword 1. If the enabled transport block is transportblock 2, the transport block 2 is mapped with codeword 0. The firstlogic value of the swap flag corresponds to 0 or off, and its secondlogic value corresponds to 1 or on. The first and second logic valuesmay have, but not limited to, a random type of 1/0 or on/off. In otherwords, the first logic value may correspond to 1 or on, and the secondlogic value may correspond to 0 or off. This definition of the first andsecond logic values can equally be applied to other fields according tothe following embodiment.

Table 6 and Table 7 illustrate transport block to codeword mappingaccording to the first embodiment.

TABLE 6 TB to CW mapping swap flag (one TB enabled) = 0 TB 1 TB 2 CW 0CW 1 enabled Disabled TB 1 — disabled enabled — TB 2

TABLE 7 TB to CW mapping swap flag (one TB enabled) = 1 TB 1 TB 2 CW 0CW 1 enabled Disabled — TB 1 Disabled enabled TB 2 —

In the second embodiment, the transport block to codeword swap flag isused as a codeword indicator.

According to this embodiment, if only one of two transport blocks isenabled, the transport block to codeword swap flag is not reserved and 1bit value is given. In a state that only one of two transport blocks isenabled, if a logic value of the swap flag is a first value (0 or off),it can be defined that the enabled transport block is mapped withcodeword 0. Meanwhile, in a state that only one of two transport blocksis enabled, if a logic value of the swap flag is a second value (1 oron), it can be defined that the enabled transport block is codeword 1.Table 8 and Table 9 illustrate transport block to codeword mappingaccording to the second embodiment.

TABLE 8 TB to CW mapping swap flag (one TB enabled) = 0 TB 1 TB 2 CW 0(enabled) CW 1 (disabled) enabled Disabled TB 1 — disabled enabled TB 2—

TABLE 9 TB to CW mapping swap flag (one TB enabled) = 1 TB 1 TB 2 CW 0(disabled) CW 1 (enabled) enabled Disabled — TB 1 disabled enabled — TB2

In the third embodiment, the transport block to codeword swap flag isused as a layer indicator.

According to this embodiment, in a state that only one of two transportblocks is enabled and the other one is disabled, if a logic value of theswap flag is a first value (0 or off), it can be defined that the userequipment acquires channel information of a first layer. And, if thelogic value of the swap flag is a second value (1 or on), it can bedefined that the user equipment acquires channel information of a secondlayer.

Meanwhile, in a state that only one of two transport blocks is enabled,if transmission is indicated by the transmit diversity scheme, thetransmit diversity scheme based on the second layer can be used. Theuser equipment can acquire channel information of two channels from adedicated reference signal transmitted through each layer. In this case,the codeword to layer mapping can follow the mapping rule of Table 4.

In the fourth embodiment, a new data indicator (NDI) or a redundancyversion (RV) field of the disabled transport block is used as a layerindicator or an antenna port indicator.

As described above, in the DCI format 2A, MCS, NDI and RV field aredefined for the transport blocks. If one of two transport blocks isenabled and the other one is disabled, the NDI field or RV field of thedisabled transport block can be used for another usage. As describedabove, if the MCS index value of the transport block is 0, or if the MCSindex value is 0 and the RV value is 1, it can be defined that thecorresponding transport block is disabled.

Since maximum two layers are used in the dual layer beamforming scheme,the base station can indicate one of two layers, which is used forsingle antenna port transmission, or antenna port, by using a 1-bitfield of the DCI. For example, as illustrated in Table 1, if the NDIvalue of the disabled transport block is a first value (or 0), itindicates that the layer used for transmission is the first layer. Ifthe NDI value of the disabled transport block is a second value (or 1),it indicates that the layer used for transmission is the second layer.

TABLE 10 Indication of antenna port(or layer) for single-antenna port(or layer) transmission (one TB disabled) New Data Indicator of thedisabled TB Antenna port(or layer) 0 1^(st) antenna port (or layer) 12^(nd) antenna port (or layer)

Meanwhile, layer indication may be performed using the RV field insteadof the NDI field of the disabled transport block. It is supposed that ifthe MCS index value of the transport block is 0, it indicates that thetransport block is disabled. In this case, it may be defined that if theRV field value of the disabled transport block is the first value (or0), it indicates the first layer. It may also be defined that if the RVfield value of the disabled transport block is the second value (or 1),it indicates the second layer.

In the fifth embodiment, a new data indicator (NDI) or a redundancyversion (RV) field of the disabled transport block is used as anindicator as to transmit diversity transmission.

As described above, if two antenna ports are used, a precodinginformation field of the DCI format 2A is not defined. If the DCI format2A is used for dual layer beamforming, uncertainty in rank 1transmission occurs. In other words, according to definition of theexisting DCI format 2A, if the precoding information field is notdefined, whether rank 1 beamforming or rank 2 beamforming is performedcan be identified by identifying whether two codewords are all enabled.In this respect, transmission according to the transmit diversity schemeis needed to be defined in the dual layer beamforming scheme. Since thetransmit diversity scheme corresponds to rank 1 transmission, whetherrank 1 beamforming or transmit diversity scheme is performed cannot beidentified by the fact that one codeword which is disabled. Accordingly,if one codeword is disabled, the NDI or RV field of the disabledtransport block can be used to identify whether transmit diversitytransmission or rank 1 beamforming is performed. For example, if the NDIvalue of the disabled transport block is the first value (or 0), itindicates transmit diversity transmission. If the NDI value of thedisabled transport block is the second value (or 1), it indicates rank 1beamforming. In case of transmit diversity transmission, the userequipment may perform data demodulation by using either a cell-specificreference signal or a dedicated reference signal for transmission of twolayers.

In the sixth embodiment, the transport block to codeword swap flag isused as an indicator indicating a transmission scheme.

According to this embodiment, if only one of two transport blocks isenabled, the transport block to codeword swap flag is not reserved, andeither a transmit diversity scheme or single layer beamforming schemecan be indicated depending on the value of the swap flag. For example,if the swap flag is the first value, it indicates the transmit diversityscheme. If the swap flag is the second value, it indicates the singlelayer beamforming scheme.

In the seventh embodiment, the precoding information field defined inthe DCI format 2A is newly defined for dual layer beamforming.

In the DCI format 2A, the precoding information field is set to 0 bit incase of transmission using two antenna ports, and is set to 2 bits incase of transmission using four antenna ports. Since maximum two antennaports are used in the dual layer beamforming transmission mode, noprecoding information field is needed as described above. Accordingly,the precoding information field can be set to 0. Even though a bit forthe precoding information field is allocated in the dual layerbeamforming transmission mode, it will not be defined.

Meanwhile, bit fields (for example, bit fields 2 and 3 if one codewordis enabled, and bit field 3 if two codewords are enabled) reserved fromthe precoding information field for four antenna ports exist in theexisting DCI format 2A as illustrated in Table 5. These reserved bitfields may be defined for dual layer beamforming.

According to the aforementioned DCI format 2A, if only one of twocodewords is enabled as described above, it may be defined that it meanssingle layer precoding, or it may be defined that it means the transmitdiversity scheme. Accordingly, if only one of two codewords is enabledas illustrated in Table 11 below, it may explicitly indicate ‘singlelayer precoding’ through a predetermined bit value of the precodinginformation field for four antenna ports.

TABLE 11 One codeword: Two codewords: Codeword 0 enabled, Codeword 0enabled, Codeword 1 disabled Codeword 1 enabled Bit Bit field fieldmapped mapped to to index Message index Message 0 4 layers: Transmit 0 2layers: precoder diversity cycling with large delay CDD 1 2 layers:precoder 1 3 layers: precoder cycling with large cycling with largedelay CDD delay CDD 2 Single layer 2 4 layers: precoder precodingcycling with large delay CDD 3 reserved 3 Reserved

Alternatively, it may indicate single layer precoding from the precodinginformation field for four antenna ports and at the same time indicatewhether the layer corresponding to single layer precoding is the firstlayer or the second layer (layer 0 or layer 1) as illustrated in Table12 below.

TABLE 12 One codeword: Two codewords: Codeword 0 enabled, Codeword 0enabled, Codeword 1 disabled Codeword 1 enabled Bit Bit field fieldmapped mapped to to index Message index Message 0 4 layers: Transmit 0 2layers: precoding diversity without CDD 1 Single layer 1 — precoding(layer 0) 2 Single layer 2 — precoding (layer 1) 3 — 3 —

In Table 12, if only one codeword is enabled, a bit field 0 of theprecoding information field indicates transmit diversity. In this case,the user equipment can perform data demodulation by using either acell-specific reference signal or a dedicated reference signal fortransmission of two layers.

According to the aforementioned embodiment of the present invention, aDCI format that can support SU-MIMO and MU-MIMO at the same time throughdual layer beamforming is provided. In other words, the DCI formats usedfor dual layer beamforming and single layer beamforming have the samebit field size.

Next, new definition of a bit field of the DCI format 1A or the DCIformat 1D, which corresponds to the exiting DCI format, in accordancewith another embodiment of the present invention will be described withreference to FIG. 4 and FIG. 5.

FIG. 4 is a diagram illustrating a DCI format 1A defined in the existing3GPP LTE standard (Release 8). The DCI format 1A is defined for compactscheduling of one PDSCH codeword in various transmission modes, and canbe used for transmit diversity transmission. This DCI format 1A can bedefined newly for dual layer beamforming. If dual layer beamforming isdefined as a transmission mode (as described above, transmission mode isset semi-statically by upper layer signaling), the user equipment candefine a part of bit fields of the aforementioned DCI format 1Adifferently from the transmit diversity scheme.

Among the fields defined in the DCI format 1A, a ‘flag for format0/format 1A differentiation’ field is set to 1 bit, wherein a value of 0in the ‘flag for format 0/format 1A differentiation’ field representsformat 0, and a value of 0 therein represents format 1A. The format 1Ais used for a random access procedure initiated by PDCCH order only ifthe format 1A CRC is scrambled with C-RNTI.

Also, among the fields defined in the DCI format 1A, a‘localized/distributed VRB assignment flag’ field is set to 1 bit. Ifthe ‘flag for format 0/format 1A differentiation’ field is set to 1, the‘localized/distributed VRB assignment flag’ field is set to 0. In othercase, a value of 0 in the ‘localized/distributed VRB assignment flag’field represents localized VRB assignment, and a value of 1 thereinrepresents distributed VRB assignment.

In the first embodiment, the ‘flag for format 0/format 1Adifferentiation’ field is newly defined for dual layer beamforming. Forexample, if a logic value of the ‘flag for format 0/format 1Adifferentiation’ field is the first value, it indicates transmitdiversity transmission. If a logic value of the ‘flag for format0/format 1A differentiation’ field is the second value, it indicatessingle layer beamforming transmission. As described above, the firstvalue of the logic value of any one of the bit fields represents 0 oroff while the second value represents 1 or on. Also, the first value ofthe logic value of any one of the bit fields may represent 1 or on whilethe second value may represent 0 or off.

Alternatively, if the logic value of the ‘flag for format 0/format 1Adifferentiation’ field is the first value, it may be newly defined thatit indicates the first layer (layer 0) in the dedicated reference signalpattern. If the logic value of the ‘flag for format 0/format 1Adifferentiation’ field is the second value, it may also be newly definedthat it indicates the second layer (layer 1).

In the second embodiment, the ‘localized/distributed VRB assignmentflag’ field is newly defined for dual layer beamforming.

For example, if a logic value of the ‘localized/distributed VRBassignment flag’ field is the first value, it indicates transmitdiversity transmission. If the logic value of the ‘localized/distributedVRB assignment flag’ field is the second value, it indicates singlelayer beamforming transmission.

Alternatively, if the logic value of the ‘localized/distributed VRBassignment flag’ field is the first value, it may indicate the firstlayer (layer 0) in the dedicated reference signal pattern. If the logicvalue of the ‘localized/distributed VRB assignment flag’ field is thesecond value, it may indicate the second layer (layer 1).

In the third embodiment, the ‘flag for format 0/format 1Adifferentiation’ field and the ‘localized/distributed VRB assignmentflag’ field are newly defined for dual layer beamforming. For example, 1bit of 2 bits for the ‘flag for format 0/format 1A differentiation’fieldand the ‘localized/distributed VRB assignment flag’ field can indicatetransmit diversity or single layer beamforming, and the other 1 bit canrepresent the first layer or the second layer.

FIG. 5 is a diagram illustrating a DCI format 1D defined in the existing3GPP LTE standard (Release 8).

The DCI format 1D is defined for compact scheduling of one PDSCHcodeword having precoding power offset information, and can be used forMU-MIMO transmission. This DCI format 1D can be defined newly for duallayer beamforming. If dual layer beamforming is defined as atransmission mode, the user equipment can define a part of bit fields ofthe aforementioned DCI format 1D differently from the MU-MIMO scheme.

Among the fields defined in the DCI format 1D, a ‘TPMI information forprecoding’ field represents a codebook index used for transmission, andis set to 2 bits when the base station includes two antenna ports, andis set to 4 bits when the base station include four antenna ports.

In the fourth embodiment of the present invention, ‘TPMI information forprecoding’ field of the DCI format 1D can be defined newly for duallayer beamforming. Transmit diversity transmission or single layerbeamforming can be represented by 1 bit of the ‘TPMI information forprecoding’ field. If a logic value of 1 bit in the ‘TPMI information forprecoding’ field given by 2 bits or 4 bits is the first value, itindicates transmit diversity transmission. If the logic value of 1 bitin the ‘TPMI information for precoding’ field given by 2 bits or 4 bitsis the second value, it indicates single layer beamforming.

Also, if the logic value of the ‘TPMI information for precoding’ fieldof 1 bit is the first value, it may indicate the first layer (layer 0).If the logic value of the ‘TPMI information for precoding’ field of 1bit is the second value, it may indicate the second layer (layer 1).

Also, the ‘TPMI information for precoding’ field of 2 bits may be used.In this case, 1 bit may indicate transmit diversity transmission orsingle layer beamforming, and the other 1 bit may indicate the firstlayer or the second layer in the dedicated reference signal pattern.

Hereinafter, new definition of the DCI format for dual layer beamformingin accordance with another embodiment of the present invention will bedescribed.

As described above, since dual layer beamforming has maximum rank 2equivalent to the number of transport blocks used for transmission, aseparate indicator for transmission rank is not needed. In other words,disabled transport block can be determined depending on that MCS indexvalue of the transport block is set to 0 (or MCS index value is 0 and RVvalue is set to 1). Accordingly, it can be recognized implicitly thatthe user equipment corresponds to rank 1 if one of two transport blocksis disabled whereas the user equipment corresponds to rank 2 if twotransport blocks are all enabled. Also, if a dedicated reference signal(precoded UE specific reference signal) is used for each layer, a weightmatrix used for precoding is not needed. Accordingly, it is not requiredthat the precoding information field be included in the downlink controlinformation (DCI) format (namely, 0 bit is allocated to the precodinginformation field) in case of dual layer beamforming based on adedicated reference signal.

Also, if the dual layer beamforming transmission mode is used(transmission mode is set semi-statically by upper layer signaling), thededicated reference signal for dual layer beamforming is used, and theuser equipment can receive data through two layers or a single layer. Ifdual layers are used, the user equipment can be operated in accordancewith the SU-MIMO mode. If a single layer is used, the user equipment canbe operated in accordance with the SU-MIMO mode or the MU-MIMO mode. Itis considered that the same DCI format is used for the SU-MIMO mode andthe MU-MIMO mode so as not to identify the SU-MIMO mode from the MU-MIMOmode in dual layer beamforming. In other words, in dual layerbeamforming and single layer beamforming, control information istransferred by DCI having the same bit field size, and a part of bitfields used for dual layer beamforming is defined as an indicator forsingle layer beamforming. Also, if the dual layer beamformingtransmission mode is used, a compact DCI format may be defined for theuser equipment that receives single layer only.

An example of a new DCI format that satisfies the aforementionedconsiderations will be described with reference to FIG. 6. The DCIformat illustrated in FIG. 6 includes a plurality of fields the same asthose of the aforementioned DCI 2A. Hereinafter, the DCI format will bedescribed based on the difference between a new DCI format and theexisting DCI 2A format.

The DCI format of FIG. 6 provides control information for single layerbeamforming and dual layer beamforming. Resource Block Assignment, TPCcommand for PUCCH, Downlink Assignment Index, HARQ process number, MCSindex for each of transport blocks 1 and 2, new data indicator,redundancy version, and precoding information can be defined in bothmodes of single layer beamforming and dual layer beamforming. Thesefields are substantially the same as those defined in the existing DCIformat 2A. Of the fields, the precoding information field is set to 0bit as described above.

Unlike the existing DCI format 2A, the ‘transport block to codewordsswap flag’ field in the DCI format of FIG. 6 is used for dual layerbeamforming. In case of single layer beamforming transmission, the‘transport block to codewords swap flag’ field can be defined as the‘layer indicator’.

If two transport blocks are all enabled, the ‘transport block tocodewords swap flag’ field can be used as information indicating mappingrelation between the transport block and codeword, wherein the mappingrelation can be defined as illustrated in Table 1 above.

If one transport block is enabled and the other transport block isdisabled, the transport block enabled as illustrated in Table 2 can bemapped with codeword 0. In case of single layer beamforming where onlyone codeword is enabled, the ‘transport block to codewords swap flag’field is defined as the ‘layer indicator’. If a logic value of the layerindicator is the first value (0 or off), it indicates the first layer(layer X). If the logic value of the layer indicator is the second value(1 or on), it indicates the second layer (layer Y). Alternatively, inthe logic value of the layer indicator, the first value may indicate 1or on, and the second value may indicate 0 or off. Also, the first valuemay indicate the mapping relation with the first layer while the secondvalue may indicate the mapping relation with the second layer. The layerindicator can be defined as illustrated in Table 13 below.

TABLE 13 Transport block to codeword swap flag value (Layer IndicationCodeword 0 Codeword 1 flag value) (enabled) (disabled) 0 Layer X/Antennaport X 1 Layer X/Antenna port X

The ‘layer indicator’ may be designated as ‘antenna port indicator’ or‘reference signal position (RS position)’. Also, the ‘layer indicator’may be defined as indicate layer/antenna port corresponding to enabledcodeword or layer (or antenna port) where the reference signal islocated. The user equipment can identify a layer to which its usefulchannel information belongs, through information acquired through thelayer indicator.

According to the new DCI format defined in FIG. 6, since the DCI formatsfor dual layer beamforming and single layer beamforming can be set tohave the same size, dynamic mode adaptation of the SU-MIMO and theMU-MIMO and dynamic rank adaptation of rank 1 and rank 2 can beimplemented.

Next, another embodiment of a new DCI format that satisfies theaforementioned considerations will be described with reference to FIG.7. The description of the DCI format illustrated in FIG. 7, which iscommon to FIG. 6, will be omitted for conciseness.

In the DCI format of FIG. 7, the ‘transport block to codewords swapflag’ field is defined in the same manner as the existing DCI format. Inother words, the ‘transport block to codewords swap flag’ is used fordual layer beamforming, and if two codewords are all enabled, it can beused as information indicating the mapping relation between transportblock and codeword as defined in Table 1 above. Meanwhile, if onetransport block is enabled and the other transport block is disabled,the transport block enabled as illustrated in Table 2 can be mapped withcodeword 0.

In case of the DCI format of FIG. 7, as the MCS index value of thetransport block is set to 0 (or MCS index value is set to 0 and RV valueis set to 1), if one transport block is enabled and the other onetransport block is disabled, the user equipment can implicitly recognizesingle layer beamforming transmission.

The new data indicator (NDI) field for the disabled transport block canbe defined as the layer indicator of the enabled transport block. Forexample, if transport block 1 is enabled and transport block 2 isdisabled, the NDI of the transport block 1 indicates whether datatransmitted through the enabled transport block 1 are new data orretransmitted data, and the NDI field of the transport block 2 can bedefined as the layer indicator (or antenna port indicator/referencesignal position) for the transport block 1. For example, if a logicvalue of the NDI of the disabled transport block is the first value (0or off), it indicates the first layer (layer X) or the first antennaport (antenna port X). If the logic value of the NDI of the disabledtransport block is the second value (1 or on), it indicates the secondlayer (layer Y) or the second antenna port (antenna port Y).Alternatively, the first value of the logic value of the NDI field mayindicate 1 or on, and the second value may indicate 0 or off. Also, thefirst value may indicate the mapping relation with the first layer whilethe second value may indicate the mapping relation with the secondlayer. The user equipment can identify a layer to which its usefulchannel information belongs, through information acquired through thelayer indicator. This layer indicator can be defined as illustrated inTable 14 below.

TABLE 14 New data indicator of disabled Codeword 0 Codeword 1 transportblock (enabled) (disabled) 0 Layer X/Antenna port X 1 Layer Y/Antennaport Y

According to the new DCI format defined in FIG. 7, since the DCI formatsfor dual layer beamforming and single layer beamforming can be set tohave the same size, dynamic mode adaptation of the SU-MIMO and theMU-MIMO and dynamic rank adaptation of rank 1 and rank 2 can beimplemented.

Next, other embodiment of a new DCI format that satisfies theaforementioned considerations will be described with reference to FIG.8. The description of the DCI format illustrated in FIG. 8, which iscommon to FIG. 6, will be omitted for conciseness.

Unlike the existing DCI format 2A, the ‘transport block to codewordsswap flag’ field is not defined in the DCI format of FIG. 8. If twocodewords are all enabled, the codeword 0 is mapped with transport block1 and the codeword 1 is mapped with transport 2.

Meanwhile, if one transport block is enabled and the other transportblock is disabled, the transport block enabled as illustrated in Table 2can be mapped with codeword 0.

In case of the DCI format of FIG. 8, as the MCS index value of thetransport block is set to 0 (or MCS index value is set to 0 and RV valueis set to 1), if one transport block is enabled and the other onetransport block is disabled, the user equipment can implicitly recognizesingle layer beamforming transmission.

The new data indicator (NDI) field for the disabled transport block canbe defined as the layer indicator of the enabled transport block. Forexample, if the transport block 1 is enabled and the transport block 2is disabled, the NDI of the transport block 1 indicates whether datatransmitted through the enabled transport block 1 are new data orretransmitted data, and the NDI field of the transport block 2 can bedefined as the layer indicator (or antenna port indicator/referencesignal position) for the transport block 1. For example, if a logicvalue of the NDI of the disabled transport block is the first value (0or off), it indicates the first layer (layer X) or the first antennaport (antenna port X). If the logic value of the NDI of the disabledtransport block is the second value (1 or on), it indicates the secondlayer (layer Y) or the second antenna port (antenna port Y).Alternatively, the first value of the logic value of the NDI field mayindicate 1 or on, and the second value may indicate 0 or off. Also, thefirst value may indicate the mapping relation with the first layer whilethe second value may indicate the mapping relation with the secondlayer. The user equipment can identify a layer to which its usefulchannel information belongs, through information acquired through thelayer indicator. This layer indicator can be defined as illustrated inTable 14 above.

According to the new DCI format defined in FIG. 8, since the DCI formatsfor dual layer beamforming and single layer beamforming can be set tohave the same size, dynamic mode adaptation of the SU-MIMO and theMU-MIMO and dynamic rank adaptation of rank 1 and rank 2 can beimplemented.

The DCI formats described with reference to FIG. 6 to FIG. 8 can bedesignated as DCI formats 2B different from the existing DCI formats 2and 2A, and the antenna ports X and Y used for dual layer beamformingcan be designated as antenna ports 7 and 8 different from those definedin the existing LTE standard.

According to various embodiments of the present invention, in order tosupport dual layer beamforming, the existing DCI format can be definednewly or a new DCI format different from the existing DCI format can bedefined, whereby downlink control information can be provided to theuser equipment. In particular, in dual layer beamforming, the userequipment can implicitly identify whether any one of two transportblocks is disabled, through the MCS field of the transport block withoutrank information through an explicit rank indicator. Also, in dual layerbeamforming transmission, information of 1 bit is required to indicatelayer (antenna port) used for transmission. In this case, the NDI bitfield for the disabled one two transport blocks can be used to indicatethe layer, whereby transmission for two user equipments that use asingle layer can be supported.

FIG. 9 is a diagram illustrating a configuration of a preferredembodiment of a user equipment according to the present invention.

Referring to FIG. 9, the user equipment includes a receiving module 910,a transmitting module 920, a processor 930, and a memory 940. Thereceiving module 910 can receive various signals, data and informationfrom a base station. The transmitting module 920 can transmit varioussignals, data and information to the base station. In this embodiment,the user equipment can receive a downlink signal from the base stationin a MIMO system that supports dual layer transmission based on firstand second antenna ports. The processor 930 of the user equipmentperforms a control operation so that the receiving module 910 receivesdownlink control information (DCI) through a downlink control channel,and receives downlink data through a downlink data channel, wherein thedownlink data include one or more of first and second transport blocks.The downlink control information includes a new data indicator (NDI) foreach of the first and second transport blocks. If the first transportblock is disabled and the second transport block is enabled, the NDI forthe first transport block indicates an antenna port through which thesecond transport block is received.

In addition, the processor 930 performs an operation function forinformation received by the user equipment and information to betransmitted from the user equipment to the outside. The memory 940stores the operated information for a predetermined time period therein,and can be replaced with another module such as a buffer (not shown).

FIG. 10 is a diagram illustrating a configuration of a preferredembodiment of a base station according to the present invention.

Referring to FIG. 10, the base station includes a receiving module 1010,a transmitting module 1020, a processor 1030, and a memory 1040. Thetransmitting module 1020 can transmit various signals, data andinformation to the user equipment. The receiving module 1010 can receivevarious signals, data and information from the user equipment. In thisembodiment, the base station can transmit a downlink signal to the userequipment in a MIMO system that supports dual layer transmission basedon first and second antenna ports. The processor 1030 of the basestation performs a control operation so that the transmitting module1020 transmits downlink control information (DCI) through a downlinkcontrol channel, and transmits downlink data through a downlink datachannel, wherein the downlink data include one or more of first andsecond transport blocks. The downlink control information includes a newdata indicator (NDI) for each of the first and second transport blocks.If the first transport block is disabled and the second transport blockis enabled, the NDI for the first transport block indicates an antennaport through which the second transport block is transmitted.

In addition, the processor 1030 performs an operation function forinformation received by the base station and information to betransmitted from the base station to the outside. The memory 1040 storesthe operated information for a predetermined time period therein, andcan be replaced with another module such as a buffer (not shown).

The aforementioned embodiments according to the present invention can beimplemented by various means, for example, hardware, firmware, software,or their combination.

If the embodiment according to the present invention is implemented byhardware, the embodiment of the present invention can be implemented byone or more application specific integrated circuits (ASICs), digitalsignal processors (DSPs), digital signal processing devices (DSPDs),programmable logic devices (PLDs), field programmable gate arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

If the embodiment according to the present invention is implemented byfirmware or software, the embodiment of the present invention can beimplemented by a type of a module, a procedure, or a function, whichperforms functions or operations described as above. A software code maybe stored in a memory unit and then may be driven by a processor. Thememory unit may be located inside or outside the processor to transmitand receive data to and from the processor through various means whichare well known.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

What is claimed is:
 1. A method for receiving a downlink signal from abase station to a user equipment in a multiple input multiple output(MIMO) system that supports dual layer transmission based on first andsecond antenna ports, the method comprising: receiving downlink controlinformation (DCI) through a downlink control channel; and receivingdownlink data through a downlink data channel, the downlink dataincluding at least a first transport block or a second transport block,wherein the downlink control information includes a new data indicator(NDI) for each of the first and second transport blocks, wherein, whenthe downlink control information indicates that the first transportblock is disabled and the second transport block is enabled, the newdata indicator for the first transport block indicates an antenna portthrough which the second transport block is received among the first andsecond antenna ports, wherein the new data indicator is given by 1 bit,and the antenna port through which the second transport block isreceived is indicated by the 1-bit new data indicator for the firsttransport block, and wherein the first and second antenna portscorrespond, respectively, to first and second layers for the dual layertransmission of the first and second transport blocks.
 2. The method ofclaim 1, wherein, when the new data indicator for the first transportblock has a first value, the first antenna port for the second transportblock is indicated, and wherein, when the new data indicator for thefirst transport block has a second value, the second antenna port forthe second transport block is indicated.
 3. The method of claim 1,wherein the second transport block is mapped to one of first and secondcodewords, wherein one codeword mapped to the second transport block ismapped to one of the first and second layers, and wherein the one of thefirst and second layers mapped to the one codeword, which is mapped tothe second transport block, corresponds to one of the first and secondantenna ports.
 4. The method of claim 1, wherein the downlink controlinformation further includes modulation and coding scheme (MCS) for eachof the first and second transport blocks, and the modulation and codingscheme (MCS) is used for determining whether a corresponding transportblock is disabled.
 5. The method of claim 1, further comprisingreceiving a UE-specific reference signal for demodulating the downlinkdata for at least the first antenna port or the second antenna port. 6.The method of claim 1, wherein the downlink data channel is a physicaldownlink common channel (PDSCH), and the downlink control channel is aphysical downlink control channel (PDCCH).
 7. A method for transmittinga downlink signal from a base station to a user equipment in a multipleinput multiple output (MIMO) system that supports dual layertransmission based on first and second antenna ports, the methodcomprising: transmitting downlink control information (DCI) through adownlink control channel; and transmitting downlink data through adownlink data channel, the downlink data including at least a firsttransport block or a second transport block, wherein the downlinkcontrol information includes a new data indicator (NDI) for each of thefirst and second transport blocks, wherein, when the downlink controlinformation indicates that the first transport block is disabled and thesecond transport block is enabled, the new data indicator for the firsttransport block indicates an antenna port through which the secondtransport block is transmitted among the first and second antenna ports,wherein the new data indicator is given by 1 bit, and the antenna portthrough which the second transport block is transmitted is indicated bythe 1-bit new data indicator for the first transport block, and whereinthe first and second antenna ports correspond, respectively, to firstand second layers for the dual layer transmission of the first andsecond transport blocks.
 8. The method of claim 7, wherein, when the newdata indicator for the first transport block has a first value, thefirst antenna port for the second transport block is indicated, andwherein, when the new data indicator for the first transport block has asecond value, the second antenna port for the second transport block isindicated.
 9. The method of claim 7, wherein the second transport blockis mapped to one of first and second codewords, wherein one codewordmapped to the second transport block is mapped to one of the first andsecond layers, and wherein the one of the first and second layers mappedto the one codeword, which is mapped to the second transport block,corresponds to one of the first and second antenna ports.
 10. The methodof claim 7, wherein the downlink control information further includesmodulation and coding scheme (MCS) for each of the first and secondtransport blocks, and the modulation and coding scheme (MCS) is used fordetermining whether a corresponding transport block is disabled.
 11. Themethod of claim 7, further comprising transmitting a UE-specificreference signal for demodulating the downlink data for at least thefirst antenna port or the second antenna port.
 12. The method of claim7, wherein the downlink data channel is a physical downlink commonchannel (PDSCH), and the downlink control channel is a physical downlinkcontrol channel (PDCCH).
 13. A user equipment for receiving a downlinksignal from a base station in a multiple input multiple output (MIMO)system that supports dual layer transmission based on first and secondantenna ports, the user equipment comprising: a receiving modulereceiving control information and data from the base station; atransmitting module transmitting control information and data to thebase station; and a processor connected with the receiving module andthe transmitting module, controlling the user equipment including thereceiving module and the transmitting module, wherein the processor isconfigured to: control the receiving module to receive downlink controlinformation (DCI) through a downlink control channel, and control thereceiving module to receive downlink data through a downlink datachannel, the downlink data including at least a first transport block ora second transport block, wherein the downlink control informationincludes a new data indicator (NDI) for each of the first and secondtransport blocks, wherein, when the downlink control informationindicates that the first transport block is disabled and the secondtransport block is enabled, the new data indicator for the firsttransport block indicates an antenna port through which the secondtransport block is received among the first and second antenna ports,wherein the new data indicator is given by 1 bit, and the antenna portthrough which the second transport block is received is indicated by the1-bit new data indicator for the first transport block, and wherein thefirst and second antenna ports correspond, respectively, to first andsecond layers for the dual layer transmission of the first and secondtransport blocks.
 14. A base station for transmitting a downlink signalto a user equipment in a multiple input multiple output (MIMO) systemthat supports dual layer transmission based on first and second antennaports, the base station comprising: a receiving module receiving controlinformation and data from the user equipment; a transmitting moduletransmitting control information and data to the user equipment; and aprocessor connected with the receiving module and the transmittingmodule, controlling the base station including the receiving module andthe transmitting module, wherein the processor is configured to: controlthe transmitting module to transmit downlink control information (DCI)through a downlink control channel, and control the transmitting moduleto transmit downlink data through a downlink data channel, the downlinkdata including at least a first transport block or a second transportblock, wherein the downlink control information includes a new dataindicator (NDI) for each of the first and second transport blocks,wherein, when the downlink control information indicates that the firsttransport block is disabled and the second transport block is enabled,the new data indicator for the first transport block indicates anantenna port through which the second transport block is transmittedamong the first and second antenna ports, wherein the new data indicatoris given by 1 bit, and the antenna port through which the secondtransport block is transmitted is indicated by the 1-bit new dataindicator for the first transport block, and wherein the first andsecond antenna ports correspond, respectively, to first and secondlayers for the dual layer transmission of the first and second transportblocks.